Communication in Parallel Algorithms for Constraint-Based Local Search

Abstract : We address the issue of parallelizing constraint solvers based on local search methods for massively parallel architectures, involving several thousands of CPUs. We present a family of a constraint-based local search algorithms and investigate their performance results on hardwares with several hundreds of processors. The first method is a basic independent multiple-walk algorithm: each processor runs a local search starting from a distinct initial configuration and the first one which will reach a solution will notify the others and stop all computations. These simple methods have good performances, and good speedups can be achieved up to a few hundreds of processors. Then we consider 2 versions with communication between processors: 1) every $c$ iterations, each processor sends the current value (cost) of its configuration to others and a processor who received a better cost from another processor can decide to stop its current search with a probability $p$; 2) the number of iterations corresponding to the cost is also transfered. Both the received cost and the number of iterations have to be better for a processor to decide to draw a probability and restart. Several experiments involving more than 100 processors have been conducted and different values of $p$ have been tried to consider more or less "autistic" processors. However results show that it is very difficult to achieve better performance than the initial method without communication.
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https://hal.inria.fr/hal-00751702
Contributor : Yves Caniou <>
Submitted on : Wednesday, November 14, 2012 - 9:29:12 AM
Last modification on : Saturday, June 29, 2019 - 1:30:55 AM

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  • HAL Id : hal-00751702, version 1

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Yves Caniou, Philippe Codognet. Communication in Parallel Algorithms for Constraint-Based Local Search. PCO - IEEE Workshop on new trends in Parallel Computing and Optimization in conjonction with IPDPS, May 2011, Anchorage, United States. ⟨hal-00751702⟩

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